Our British Patent No. 2082941 discloses a separator which is particularly suitable for separating, for example, sewage and other solid matter from water in storm water overflows. The separator is in the form of a cylindrical vessel having an inlet which is disposed tangentially so as to promote a circulating flow within the vessel. This circulating flow comprises an outer, relatively fast, flow and an inner, relatively slow, flow. The shear zone between these two regions is stabilised by an annular dip plate which projects downwardly from the top of the vessel. A flow modifying member is provided in the vessel to enhance the removal of solid particles accumulating at the bottom of the vessel to a central outlet. Clean water is removed from the top of the vessel. In the vessel shown in our British Patent No. 2082941, a floatables trap is provided directly above the inlet and opposite the outlet in order to reduce the possibility of floatable solids being discharged through the clean water outlet. It is specifically stated that the trap should be disposed anywhere around the circumference of the vortex chamber.
It has been found that, under storm conditions, the floatables trap of the separator disclosed in our British Patent No. 2082941, whilst performing satisfactorily for the majority of the time, may permit floatable material to reach the outlet, by passing under the annular dip plate. It is believed that this may occur as the separator is filling during the onset of a storm or, in the alternative, in a lull during a storm when the level of the water in the separator may drop below the level of the dip plate. Departing from the teaching of British Patent No. 2082941, it is now proposed to provide a floatables trap at an upper region of the vessel, inward of the annular dip plate.
EP-A- No. 0168538 discloses a clarifier for removing particulate matter from a liquid comprising a chamber defined by a cylindrical wall. At the upper region of the chamber there is provided a cylindrical member, vertically orientated, which extends through a top plate. Outside this cylindrical member there is provided a floatables trap. The majority of floatable material will float upwards through the slot defined between the upper rim 22 of the large truncated cone 21 and the chamber wall and be trapped by the floatables trap defined by the annular plate 9 and the outer wall 2. Other floatable material may rise within the large truncated cone 21 but it is stated that the upwardly flowing liquid follows the inner surface of the larger truncated cone 21 and therefore has a radially outward component. It is also stated that any floatables inward of the large truncated cone will tend to rise into the annular space between the dip plate 9b and the chamber wall 2. Should any floatable material not be trapped by the annular trap between plate 9b and outer wall 2, it will exit with clarified liquid and pass over the weir 9a into the trough 11 and collect in the effluent collection box 13, thereby polluting the clarified liquid.